1. Field of the Invention
This invention is related to an improvement in the structure of a screw and in particular to one which can be easily turned into a piece of hard wood.
2. Description of the Prior Art
The conventional screw consists essentially of a solid cylinder, usually of metal, around which a thread winds spirally, either clockwise or counterclockwise. However, it is difficult to turn the screw into an object if it is made of hard wood. Hence, an improved screw as shown in UK Patent No. 2040769 (see FIGS. 1A, 1B, 1C, 1D and 1E) has been designed to obviate this drawback. As shown, the screw includes a triangular shankformed with spiral triangular threads 11. The shank 1 is first processed into one with a triangular cross section and then cut with spiral threads 11. U.S. Pat. No. 5044855 (see FIGS. 2 and 2A) also discloses a screw 2 with a triangular shank with a smaller diameter at the lower end and formed with spiral triangular threads 21. However, although the spiral triangular threads 21 can facilitate the turning of the screw into the wood, it still requires a lot of effort to turn the screw because of the resistance produced by the rotation of the triangular shank in the wood thereby often making one feel utterly exhausted in order to fasten pieces of hard wood.
Therefore, it is an object of the present invention to provide an improvement in the structure of a screw which can obviate and mitigate the above-mentioned drawbacks.
This invention is related to an improvement in the structure of a screw.
According to a preferred embodiment of the present invention, a screw includes a cylindrical shank having an upper portion formed with spiral circular threads and a lower portion formed with spiral triangular threads, each of the spiral triangular threads having three budges having three sharp edges and three pointed tips, the pointed tips of the spiral triangular threads being located at different positions, the cylindrical shank having a pointed end at a lower portion thereof.
It is the primary object of the present invention to provide an improved screw which can be easily turned into a piece of hard wood.
It is another object of the present invention to provide an improved screw which is simple in construction.
It is a further object of the present invention to provide an improved screw which is inexpensive to manufacture.
The foregoing objects and summary provide only a brief introduction to the present invention. To fully appreciate these and other objects of the present invention as well as the invention itself, all of which will become apparent to those skilled in the art, the following detailed description of the invention and the claims should be read in conjunction with the accompanying drawings. Throughout the specification and drawings identical reference numerals refer to identical or similar parts. Many other advantages and features of the present invention will become manifest to those versed in the art upon making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principle of the present invention is shown by way of illustrative example.